Which type of foam should be used to combat a fire involving polar solvents?

When dealing with fires involving polar solvents, alcohol-resistant foam is the most suitable choice. Polar solvents, such as alcohols and some types of esters, have properties that can lead to difficulties in suppressing their fires with standard foams. These types of solvents can mix with water, which reduces the effectiveness of typical water-based foams and may exacerbate the situation.

Alcohol-resistant foam is specifically formulated to create a barrier between the polar solvent and the fire, thereby preventing the ignition of vapors and cooling the flames. This type of foam is designed to maintain its integrity in the presence of water-miscible substances, effectively smothering the fire and securing the area against re-ignition. Its unique formulation includes additives that allow it to retain its firefighting capabilities even when coming into contact with polar solvents.

Other foam types, such as protein foam, water-based foam, and Class A foam, do not possess the necessary properties to effectively combat fires fueled by polar solvents and may actually make the situation worse by potentially worsening the spread of the fire or failing to suppress it sufficiently. Thus, alcohol-resistant foam is clearly the correct choice for this particular firefighting scenario.